An Array Texture is a Texture where each mipmap contains a series of 1D or 2D images of the same size. Array textures are structurally similar to 3D Textures in that they have an effective "depth" component. However, filtering never takes place between the separate textures in the array, and lower mipmaps still have the same number of array layers.

Pre OpenGL 3.0, the high cost of texture switches resulted in a widespread preference for texture atlases, which result in less switching, and thus less overhead. 3.0 capable hardware attempts to overcome this by providing fast hardware texture switching capabilities via array textures; but be aware that if you are limited by the number of hardware texture units, you may still be better off using atlases (perhaps even in conjunction with array textures).

Array texture are not usable from the fixed function pipeline; you must use a Shader to access them.

Contents

Terminology

Each mipmap level of an array texture is a series of images. Each image within a mipmap is called a "layer".

Creation and Management

1D array textures are created by binding a newly-created texture object to GL_TEXTURE_1D_ARRAY, then creating storage for one or more mipmaps of the texture. This is done by using the "2D" image functions; the "height​" parameter sets the number of layers in the array texture.

Every row of pixel data in the "2D" array of pixels is considered a separate 1D layer.

2D array textures are created similarly; bind a newly-created texture object to GL_TEXTURE_2D_ARRAY, then use the "3D" image functions to allocate storage. The depth​ parameter sets the number of layers in the array.

Each 2D row/column sequence of pixel data in the "3D" array of pixels is considered a separate 2D layer.

Here is a source-code example:

GLuinttexture=0;GLuintwidth=2;GLuintheight=2;GLuintlevelCount=2;//Read you texels here. In the current example, we have 2*2*2 = 8 texels, with each texel being 4 GLubytes.GLubytetexels[32]={//Texels for first image.0,0,0,255,255,0,0,255,0,255,0,255,0,0,255,255,//Texels for second image.255,255,255,255,255,255,0,255,0,255,255,255,255,0,255,255,};glGenTextures(1,&texture);glBindTexture(GL_TEXTURE_2D_ARRAY,texture);glTexParameteri(GL_TEXTURE_2D_ARRAY,GL_TEXTURE_MIN_FILTER,GL_LINEAR);//Always set reasonable texture parametersglTexParameteri(GL_TEXTURE_2D_ARRAY,GL_TEXTURE_MAG_FILTER,GL_LINEAR);glTexParameteri(GL_TEXTURE_2D_ARRAY,GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);glTexParameteri(GL_TEXTURE_2D_ARRAY,GL_TEXTURE_WRAP_T,GL_CLAMP_TO_EDGE);glTexImage3D(GL_TEXTURE_2D_ARRAY,0,GL_RGBA8,width,height,levelCount,0,GL_RGBA,GL_UNSIGNED_BYTE,texels);

Note that, unlike for 3D Textures, each mipmap uses the same number of layers. So if you're allocating 3 mipmaps of a 2D array texture, it would look like this:

Access in shaders

Texture arrays have separate sampler types: sampler1DArray​ and sampler2DArray​. When accessing them within a shader, you use one extra texture coordinate. So sampler1DArray​ would use a 2D texture coordinate, while sampler2DArray​ would use a 3D texture coordinate.

The last coordinate is the layer number to access. For floating-point texture coordinates (when not using texture functions like texelFetch​), the floating-point layer is used to compute the integer layer index by the following function:

actual_layer = max(0, min(d​ - 1, floor(layer​ + 0.5)) )

Here, d​ is the number of layers in the texture, and layer​ is the floating-point layer from the texture coordinate.